1//
2// bitfield.c - extract and set bit fields
3//
4// Written by Eryk Vershen
5//
6// See comments in bitfield.h
7//
8
9/*
10 * Copyright 1996, 1997 by Apple Computer, Inc.
11 *              All Rights Reserved
12 *
13 * Permission to use, copy, modify, and distribute this software and
14 * its documentation for any purpose and without fee is hereby granted,
15 * provided that the above copyright notice appears in all copies and
16 * that both the copyright notice and this permission notice appear in
17 * supporting documentation.
18 *
19 * APPLE COMPUTER DISCLAIMS ALL WARRANTIES WITH REGARD TO THIS SOFTWARE
20 * INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
21 * FOR A PARTICULAR PURPOSE.
22 *
23 * IN NO EVENT SHALL APPLE COMPUTER BE LIABLE FOR ANY SPECIAL, INDIRECT, OR
24 * CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM
25 * LOSS OF USE, DATA OR PROFITS, WHETHER IN ACTION OF CONTRACT,
26 * NEGLIGENCE, OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION
27 * WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
28 */
29
30#include "bitfield.h"
31
32
33//
34// Defines
35//
36
37
38//
39// Types
40//
41
42
43//
44// Global Constants
45//
46const unsigned int masks[] = {
47    0x00000000,
48    0x00000001, 0x00000003, 0x00000007, 0x0000000F,
49    0x0000001F, 0x0000003F, 0x0000007F, 0x000000FF,
50    0x000001FF, 0x000003FF, 0x000007FF, 0x00000FFF,
51    0x00001FFF, 0x00003FFF, 0x00007FFF, 0x0000FFFF,
52    0x0001FFFF, 0x0003FFFF, 0x0007FFFF, 0x000FFFFF,
53    0x001FFFFF, 0x003FFFFF, 0x007FFFFF, 0x00FFFFFF,
54    0x01FFFFFF, 0x03FFFFFF, 0x07FFFFFF, 0x0FFFFFFF,
55    0x1FFFFFFF, 0x3FFFFFFF, 0x7FFFFFFF, 0xFFFFFFFF
56};
57
58
59//
60// Global Variables
61//
62
63
64//
65// Forward declarations
66//
67
68
69//
70// Routines
71//
72unsigned int
73bitfield_set(unsigned int *bf, int base, int length, unsigned int value)
74{
75    unsigned int t;
76    unsigned int m;
77    int s;
78
79    // compute shift & mask, coerce value to correct number of bits,
80    // zap the old bits and stuff the new value
81    // return the masked value in case someone wants it.
82    s = (base + 1) - length;
83    m = masks[length];
84    t = value & m;
85    *bf = (*bf & ~(m << s)) | (t << s);
86    return t;
87}
88
89
90unsigned int
91bitfield_get(unsigned int bf, int base, int length)
92{
93    unsigned int m;
94    int s;
95
96    // compute shift & mask
97    // return the correct number of bits (shifted to low end)
98    s = (base + 1) - length;
99    m = masks[length];
100    return ((bf >> s) & m);
101}
102